They have no obligation to pm you, why should they have to pm you first? That's a courtesy players sometimes give in case they think it's a mistake. And it doesn't matter if you don't think you're kill stealing, server rules are server rules, nobody is going to be immune because their personal beliefs make them think they are not breaking the rules. You broke the rules, you got caught, you got muted. Mutes are warnings, so people know "oh, wow, I did something wrong, better stop."